A wildfire near Yosemite National Park in California has exploded in size, prompting evacuation orders for thousands of people and shutting off power to more than 2,000 homes and businesses.

The Oak Fire, which began on Friday afternoon south-west of the park near Midpines in Mariposa County, grew to 10.2 square miles by Saturday morning, according to the California Department of Forestry and Fire Protection (Cal Fire).

Evacuation orders were put in effect for more than 6,000 people in the sparsely-populated rural area, said Daniel Patterson, a spokesman for the Sierra National Forest.

“Explosive fire behaviour is challenging firefighters,” a Cal Fire spokesperson said, describing the fire activity as “extreme with frequent runs, spot fires and group torching”.

California Wildfires
High winds cause tree canopies to flare up as a wildfire burns east of Midpines in Mariposa County (The Fresno Bee via AP)

As of Saturday morning, the fire had destroyed 10 residential and commercial structures and damaged five others, and is threatening 2,000 more.

The fast-growing blaze prompted state transport officials to order numerous road closures, including a shutdown of Highway 140 between Carstens Road and Allred Road – blocking one of the main routes into Yosemite National Park.

More than 400 firefighters, along with helicopters, other aircraft and bulldozers, battled the blaze, Mr Patterson said.

Hot weather and bone-dry vegetation caused by the worst drought in decades was fuelling the blaze and challenging fire crews, said Daniel Patterson, a spokesman for the Sierra National Forest.

“The fire is moving quickly. This fire was throwing embers out in front of itself for up to two miles yesterday,” Mr Patterson said. “These are exceptional fire conditions.”

California Wildfires
Flames engulf a chair inside a burning home as the Oak Fire burns in Mariposa County (AP)

Pacific Gas & Electric said on its website that more than 2,600 homes and businesses in the area had lost power as of Friday afternoon and there was no indication when it would be restored. “PG&E is unable to access the affected equipment,” the utility firm said.

There was no immediate word on what might have caused the fire.

Meanwhile, firefighters have made significant progress against a wildfire that began in Yosemite National Park and burned into the Sierra National Forest.

The Washburn Fire was 79% contained on Friday after burning about 7.5 square miles of forest.

The fire broke out July 7 and forced the closure of the southern entrance to Yosemite and evacuation of the community of Wawona as it burned on the edge of Mariposa Grove, home to hundreds of giant sequoias, the world’s largest trees by volume.